VBS.Krim@mm

SUMMARY

VBS.Krim@mm is a Visual Basic Script (VBS) worm that uses Microsoft Outlook MAPI to mail itself to all contacts in the Outlook address book.

Protection

• Virus Definitions (LiveUpdate™ Weekly) March 27, 2002
• Virus Definitions (Intelligent Updater) March 25, 2002

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Medium
• Large Scale E-mailing: Mails itself to all contacts in Outlook address book.
• Deletes Files: Could format drive C.

Distribution

• Distribution Level: High
• Subject of Email: MIRKO
• Name of Attachment: Mirko.bat
• Size of Attachment: 2,353 bytes

TECHNICAL DETAILS

VBS.Krim@mm arrives as an email attachment. The email has the following characteristics:

Subject: MIRKO
Message: Che stai facendo ????
Attachment: Mirko.bat

This attachment is a batch file. When it is executed, it does the following:

It creates the folder C:WindowsMk

It creates the following files:

• C:WindowsMirko.vbs
• C:WindowsMirko.reg
• C:WindowsMkMirko.vbs
• C:WindowsDesktopMirko.txt

The worm then copies itself as C:WindowsMkMirko.bat.

Next, it appends the following line to the end of the C:Autoexec.bat file:

@call C:windowssystemmirko.bat

The worm then attempts to add the value

mirko c:windowsmkmirko.bat

to the registry key

HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun

The worm then searches for the file C:WindowsDesktopMirko.txt. If the worm cannot find this file on the desktop, it begins to perform a quick format of drive C.

Next, the worm uses the file C:WindowsMirko.vbs to mail itself to all contacts in Outlook address book.

Finally, it uses C:WindowsMkMirko.vbs to display the following message:



NOTES:

• Norton AntiVirus detects both C:WindowsMkMirko.bat and C:WindowsMirko.vbs as VBS.Krim@mm.
• It does not detect C:WindowsMkMirko.vbs, C:WindowsMirko.reg, or C:WindowsDesktopMirko.txt because they are not viral.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
• Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. Perform a forensic analysis and restore the computers using trusted media.
• Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.

REMOVAL

Delete any files detected as VBS.Krim@mm, remove the value that it added to the registry, and (on Windows 95/98/Me computers) remove the line that it added to the Autoexec.bat file.

To remove this worm:

1. Obtain the most recent virus definitions. There are two ways to do this:
   • Run LiveUpdate. LiveUpdate is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
   • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions have undergone full quality assurance testing by Symantec Security Response. They are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.
     
     Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.
     
2. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files. For instructions on how to do this, read the document How to configure Norton AntiVirus to scan all files.
3. Run a full system scan.
4. Delete all files that are detected as VBS.Krim@mm.
5. Using Windows Explorer, delete C:WindowsMkMirko.vbs, C:WindowsMirko.reg, and C:WindowsDesktopMirko.txt.

To edit the registry:

CAUTION: We strongly recommend that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify only the keys that are specified. Read the document How to make a backup of the Windows registry for instructions.

1. Click Start, and click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Navigate to the following key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
4. In the right pane, delete the following value:
   
   mirko     c:windowsmkmirko.bat
   
5. Click Registry, and click Exit.

To edit the Autoexec.bat file:
This is necessary only on Windows 95/98/Me-based computers.

NOTE: (For Windows Me users only) Due to the file-protection process in Windows Me, a backup copy of the file that you are about to edit exists in the C:WindowsRecent folder. We recommend that you delete this file before you continue with the steps in this section. To do this using Windows Explorer, go to the C:WindowsRecent folder, and in the right pane select and delete the Win.ini file. It will be regenerated as a copy of the file that you are about to edit when you save your changes to that file.

1. Click Start, and click Run.
2. Type the following, and then click OK.
   
   edit c:autoexec.bat
   
   The MS-DOS Editor opens.
   
3. Delete the following line:
   
   @call C:windowssystemmirko.bat
   
4. Click File, and click Save.
5. Click File, and click Exit.